The exhaust manifold of a vehicular engine connects several exhaust ports of the engine to an exhaust pipe. The exhaust pipe then extends from the engine compartment to a muffler and tail pipe assembly. Exhaust gases generated by combustion in the engine are directed sequentially through the exhaust manifold, the exhaust pipe, the muffler and the tail pipe, and ultimately are released into the ambient surroundings. Certain engines, such as V-8's, for example, utilize a pair of exhaust manifolds. In these instances the vehicle may have two separate exhaust systems, or, alternatively the two exhaust pipes may be joined at some point intermediate the engine and the tail pipe.
One type of prior art exhaust manifold utilizes tubes to carry exhaust gases from the respective cylinders. This tubular manifold includes an inlet flange which is mounted directly on the engine cylinder head adjacent the cylinders. The inlet flange has a plurality of spaced apertures corresponding to the exhaust ports of the engine. The tubes are connected to the inlet flange, and are welded to one another so as to eventually connect into a single exhaust pipe. Although tubular exhaust manifolds generally perform well, the tubes often require complex welds and bends. These complexities are especially significant on small engines or on larger engines housed in engine compartments having a small available space envelope. For example, the presence of pollution control equipment, vehicular accessories and such may require the exhaust manifold to connect the engine exhaust ports to the exhaust pipe within a space of between two and three inches.
To fit a tubular exhaust manifold into a small engine compartment it frequently is necessary to make many precise miter cuts to the tubes, and then to subsequently weld the tubes together along the precise miter cuts. The angularly aligned welds are not well adapted for automation, and are generally carried out manually. As a result, the welding of tubular exhaust manifolds is slow and costly. Additionally, as the number and complexity of welds increases, the probability of weld defects also increases. Consequently, an extensive product checking and quality control program must be undertaken with tubular exhaust manifolds which are constructed to occupy a small space.
Another prior art exhaust manifold defines a one piece cast metal tank which includes at least one inlet and an outlet. The inlets are positioned to receive exhaust gases generated by combustion in the cylinders. The outlet is located to connect to the exhaust pipe. Cast metal manifolds efficiently transport gases and can be adapted to many sizes. However, the cast metal exhaust manifold typically weighs about twice as much as a tubular manifold for the same engine. This added weight of course affects fuel efficiency. Additionally the extra front end weight has a detrimental effect on the performance and handling of front wheel drive cars. Furthermore, it is now known that the large mass of the cast metal exhaust manifold adjacent to the engine exhaust ports acts as a heat sink and absorbs the heat of combustion. As a result, the catalytic converter lights-off more slowly and the level of harmful exhaust emitted by the vehicle increases. In certain instances, the use of a cast metal manifold necessitates the use of additional pollution control equipment such as air pumps.
In view of the above, it is an object of the subject invention to provide an exhaust manifold which is both light weight and easy to manufacture.
It is another object of the subject invention to provide an exhaust manifold which can be manufactured easily to fit in small spaces.
It is an additional object of the subject invention to provide an exhaust manifold which eliminates complex welding and bending of tubes.
It is a further object of the subject invention to provide an exhaust manifold with a configuration that is conducive to automated welding.
It is another object of the subject invention to provide an exhaust manifold which enables pollution control equipment to operate most efficiently.